1. Field of the Invention
The present invention relates to variants of TY145 subtilases and BPN′ subtilases and to methods of construction such variants with altered properties, such as stability (e.g. thermostability or storage stability), Ca2+ dependency, pH dependent activity.
2. Description of Related Art
Enzymes have been used within the detergent industry as part of washing formulations for more than 30 years. Proteases are from a commercial perspective the most relevant enzyme in such formulations, but other enzymes including lipases, amylases, cellulases, hemicellulases or mixtures of enzymes are also often used.
To improve the cost and/or the performance of proteases there is an ongoing search for proteases with altered properties, such as increased activity at low temperatures, increased thermostability, increased specific activity at a given pH, altered Ca2+ dependency, increased stability in the presence of other detergent ingredients (e.g. bleach, surfactants etc.) etc.
The search for proteases with altered properties include both discovery of naturally occurring proteases, i.e. so called wild-type proteases but also alteration of well-known proteases by e.g. genetic manipulation of the nucleic acid sequence encoding said proteases. Knowledge of the relationship between the three-dimensional structure and the function of a protein has improved the ability to evaluate which areas of a protein to alter to affect a specific characteristic of the protein.
One family of proteases, which are often used in detergents, are the subtilases. This family has previously been further grouped into 6 different sub-groups by Siezen R J and Leunissen J A M, 1997, Protein Science, 6, 501-523. One of these sub-groups is the Subtilisin family which includes subtilases such as BPN′, subtilisin 309 (SAVINASE®, Novozymes A/S), subtilisin Carlsberg (ALCALASE®, Novozymes A/S), subtilisin S41 (a subtilase from the psychrophilic Antarctic Bacillus TA41, Davail S et al. 1994, The Journal of Biological Chemistry, 269(26), 99. 17448-17453), subtilisin S39 (a subtilase from the psychrophilic Antarctic Bacillus TA39, Narinx E et al. 1997, Protein Engineering, 10 (11), pp. 1271-1279) and TY145 (a subtilase from Bacillus sp. TY145, NCIMB 40339 described in WO 92/17577).
However, despite the sequence homology between the subtilases belonging to the Subtilisin subgroup of subtilases, modelling of the three-dimensional structure of one subtilase on the basis of the three-dimensional structure of another subtilase may result in an incorrect three-dimensional structure because of structural differences.
The inventors of the present invention have elucidated the three-dimensional structure of the TY145 subtilase and found that there are several differences between this and the three-dimensional structure of BPN′ also belonging to the Subtilisin subgroup of subtilases. This surprising difference in structure makes it advantageous to use the TY145 structure as basis for homology modelling of TY145 like subtilisins, which, in turn, will improve the ability to obtain desired changes in functionality by protein engineering.
Two studies have used protein engineering to alter functionality of TY145 like subtilisins: Miyazaki K et al. 2000, J Mol Biol, 297, pp. 1015-1026 discloses enhancement of the thermostability and activity of the psychrophilic protease subtilisin S41 by methods of directed evolution.
Wintrode T L et al. 2000, Journal of Biological Chemistry, 275 (41), pp. 31635-31640 discloses conversion of a mesophilic subtilisin-like protease from Bacillus sphaericus SSII into its psychrophilic counterpart by methods of directed evolution. Wintrode et al. constructed the three-dimensional structural model of the SSII subtilase on basis of its homology with subtilisins Carlsberg, Savinase, BPN′ and Thermitase. However, according to the present invention the SSII subtilase pertain to the new group of TY145 like subtilases and thus the modelling of SSII based on the 3D structure of the BPN′ like subtilases will likely give an inaccurate result.
The differences between the three-dimensional structures of TY145 and BPN′ are confirmed by the recently published three-dimensional structure of the subtilase “sphericase” from Bacillus sphaericus (PDB NO:1EA7, Protein Data Bank). The overall structure and many details of this subtilase are very homologous to the TY145 subtilase structure.